Retrofitting unreinforced concrete masonry to resist tornado loading

Abstract

Advances in structural design and building materials have significantly increased the performance of many structures under the extreme loading conditions associated with natural disasters such as earthquakes. However, catastrophic structural failure after extreme wind events and tornadoes remains a problem which costs the insurance industry billions of dollars and results in an average loss of 200 lives per year in the United States. Accountable for many of these structural failures, buildings with walls of Unreinforced Masonry (URM) are incapable of withstanding the magnitude of forces brought on by a tornado, and the cracking or failure of just one wall can lead to the progressive collapse of the entire structure. The need to reinforce these systems is large, but retrofitting with conventional steel reinforcement is time consuming and costly; however, externally bonded Fiber Reinforced Polymer (FRP) composites represent a high strength, low cost alternative which and can be installed in a fraction of the time. This thesis investigates the use of FRPs to strengthen URM walls against both out-of-plane flexural loads and debris impact, and attempts to determine if enough strength can be added for such wall assemblies to meet the requirements of a Tornado Safe Room as dictated by FEMA. By adapting current design guidelines and extrapolating evidence on the performance of URM walls strengthened with FRP, a design guide is created which provides the tool necessary to use this innovative retrofitting technique to strengthen URM walls to satisfy both the flexural and impact resistance strength requirements for FEMA Tornado Safe Rooms.